Forensic Entomology is More than Just Blow Flies and Beetles

This noctuid caterpillar was unexpectedly found ingesting dried skin near the toenails of a cadaver.

Fans of CSI: Crime Scene Investigation and similar TV shows know that forensic entomology involves the use of insects and other arthropods in legal matters, including homicide cases. Entomologists who are properly trained can find clues about a corpse — for example, time of death and whether a body has been moved — by observing the insects on and around it.

Forensic entomologists rely on certain insects that are typically found on corpses. Blow flies, for examples, can hone in on dead animals and lay eggs within minutes, and forensic entomologists can gather clues by examining the developmental stages of the larvae and the pupae. Dermestid beetles are also associated with dead bodies. In fact, their larvae are sometimes used by museums and by taxidermists to strip the flesh off of bones.

A new study published in the Journal of Medical Entomology shows that other insects — ones that are not normally associated with human corpses — also interact with dead bodies, which may provide more clues for forensic entomologists in the future.

“Having never worked with cadavers I did not know what it was going to be like,” she said. “My concerns about working with cadavers quickly went away when I realized for us, the researchers, there is no sadness associated with these dead people. These people or their families donated their bodies because they wanted them to be used for education, training, and research, so to fulfill their wishes we should all try to do the best science that we can.”

Natalie’s schedule was rigorous, as she and her colleagues checked the cadavers one to four times each day for a whole year.

“I was pretty much married to my cadaver research for that year,” she said. “I made myself comfortable and brought a lawn chair to sit in for taking observation notes, changing camera lenses, and for getting the insects from the kill jar into the labeled falcon tubes.”

In two of the case studies, the researchers observed insect interactions that had not been previously documented on human cadavers. In the first one, scorpionflies (Panorpa nuptialis) were the first insects to feed upon a freshly placed cadaver. According to Natalie:

“In the fall of 2009 we had just placed a clothed cadaver face down and were waiting for the first insects to arrive so that we could catch and document them. The first insect to show up was a scorpionfly, and it landed right next to the cadaver and then crawled onto it. I knew very little about scorpionflies and initially thought it was an incidental insect that was not there for the cadaver, but I was wrong! It walked up to the head and began feeding intently on the fluids seeping from where the brain had been removed during autopsy. As we sat there watching, other scorpionflies came to the cadaver and started mating and feeding on the cadaver too. We had surveyed several cadavers prior to this one and had expected blow flies, flesh flies, and house flies to arrive first and be the most numerous. But to our surprise, for the first few visits to this cadaver, scorpionflies outnumbered all other insects.”

“It’s significant that Panorpidae (scorpionflies) were the first insects to feed upon a freshly-placed corpse,” said Dr. Jason Byrd, President-Elect of the North American Forensic Entomology Association, who was not involved with the research. “Entomologists rely on insect succession to help them determine portions of the postmortem interval, and having a study that indicates that Panorpidae are early-arriving species will certainly assist forensic entomologists in their investigations.”

In another case, Natalie and her colleagues saw a caterpillar (Spodoptera latifascia) in the family Noctuidae chewing and ingesting dried human skin:

“One cadaver that was still somewhat fresh had many of his toenails removed when no one was around. We hypothesized that some animal from the woods had come in and chewed/pull them off during the night, but the cameras did not catch the activity. Interestingly, the porous, soft flesh that had been previously covered by the toenails had filled with bright-red blood, so that from a distance these feet appeared to have brightly-painted toenails. Due to this phenomenon, any time I walked by this cadaver, even if it was not his turn for observations and collections, I could not help but to stare at his toes. On this day, I was walking by and could see from a distance that there was a caterpillar on his toes, so I scrapped my usual order of observations and went to see what this caterpillar was doing. I had seen caterpillars on roadkill before, but they appeared to be incidental, just in the wrong place at the wrong time. I sat and watched this caterpillar crawl around on the toes, and then it settled and began to chew and ingest the flakes of rough skin next to where the toenail had once been in the same manner that a caterpillar chews down the side of a leaf. Luckily, I had my macro lens on my camera and I got great shots of this behavior to show others, because I knew that they would not believe me otherwise! If I had been earlier or later in my observations that day, or had not stopped and watched what this caterpillar was doing without disturbing it, then I would have missed that it was actually interacting with the cadaver and was not incidental.”

A noctuid caterpillar ingesting dried skin near the toenail of a cadaver.

“The report of the noctuid caterpillar found chewing and ingesting dried human skin is interesting because we need to interpret the various postmortem artefacts that manifest on human remains,” said Dr. Byrd. “Roaches, ants, crayfish, starfish, bees, and wasps all leave characteristic markings as a result of their scavenging behavior. Knowledge that a noctuid is an opportunistic scavenger will be beneficial to entomologists because the pattern of scavenging is likely different than that of other insects, and it should not be accidentally attributed to a pattern injury from a human perpetrator.”

After her field research was completed, Natalie hit the books to find out whether her observations were new or unusual.

“It was a different kind of fun to get into the literature and try to figure out if others had reported these species interacting with cadavers or carrion and under what circumstances. I spent months and befriended our lovely librarian Bette Craig trying to answer those questions. I did not want anybody else to have to start from ground zero on a literature review if one of these species, or a closely related species, is found in association with a casework or research cadaver. I sincerely hope that this article contributes to our understanding of decomposition ecology and motivates others to observe and collect insects we usually think of as incidental during decomposition studies.”

Newer ›

Are these cadaver research sites generally in the same location or are these insect behaviors replicated in other sites in the same basic geographic area? Is repeated research supplying these species with an unnatural food source creating a new behavior?

Behaviors and life cycles of some insects — like blow flies — are pretty constant under similar conditions, like temperature. But there are many arthropods that simply haven’t been studied in this regard. Jason Byrd, the forensic entomologist mentioned above, wrote that “basic observational studies that illustrate the simple presence and/or absence of particular species helps our scientific understanding of other species … Any novel insect interaction with decomposition tissue should be reported as a simple observational study. Carrion ecology is not well understood, and the role some species play is completely unknown. So anything that will assist in basic ecological documentation is valuable in the field of forensic entomology. With our scant understanding of insect interaction on decomposing remains, anything could be important information that may play a critical factor in a legal investigation.”